In the past, semi-conducting films have been employed in the manufacture of electronic devices whose conductivity is modulated by the nature of the chemical substances present in the ambient environment in which the devices are located. By way of example, and typically, a small voltage is applied to electrodes of these devices, resulting in the generation of a current whose magnitude depends upon the conductivity of the film employed in their fabrication. The conductivity of the film, in turn, depends upon the nature of the chemicals which are in contact with it. Consequently, the change in conductivity provides a method by which the presence and amount of chemical substances in the device's environment can readily be determined.
In the past, however, such films have been subject to degradation, and a further problem has been the limited conductivity of the films. Both these characteristics have curtailed the sensitivity of the devices, making it difficult to measure accurately the electrical differences due to the presence of environmental chemical substances.
A notable improvement in the electrical sensitivities of such devices was made possible by the use of the films taught in U.S. Pat. No. 4,900,817, which employs, for example, amphiphilic oligomers formed from phthalocyanine rings, the coordinating atoms of which are coupled through oxygen linkages to provide a plurality of parallel rings. The coordinating atoms of each of the outermost rings of such oligomers are coupled, respectively, to a hydrophilic ligand and to a hydrophobic ligand, and a solution of the oligomers is formed into the desired film by deposition of it on an aqueous subphase of a Langmuir-Blodgett balance where the hydrophilic ligand moves into association with the subphase, while the hydrophobic ligand is repelled by the subphase. Such combined effects effectively align the rings parallel to the surface of the subphase.
After evaporation of the solvent and the subsequent compression of the oligomer molecules on the subphase, a substrate can be coated with multiple layers of the film formed by the compressed molecules simply by passing the substrate repeatedly through the film, for instance in a vertical direction. During each pass, the film orients itself relative to the substrate so that the surfaces having like characteristics are in association with each other, e.g., hydrophobic ligand to hydrophobic ligand, and hydrophilic ligand to hydrophilic ligand.
While the films described are useful for the purposes mentioned, they have inherent characteristics which make them relatively unsuitable for certain uses including some of those contemplated with the films taught herein.
For example, and with reference to the hydrophobic ligands responsible for assisting in the proper orientation of the phthalocyanine rings parallel to the subphase of the balance, the required hydrophobicity is made possible through the presence of relatively long aliphatic chains. When the hydrophobic axial ligands of the oligomer molecules pair together as described during formation of adjacent film layers, these chains form regions of hydrocarbon appendages that impede electron transfer. This tends to make the use of such films inappropriate for some of the newer electronic devices that depend upon anisotropic properties for their proper functioning.
An example of such a device comprises a Langmuir-Blodgett structure fabricated from a plurality of amphiphilic phthalocyanine layers, L storages incorporated in a laminate structure formed between top and bottom electrodes, at least one of which is semi-transparent. Interspersed between the phthalocyanine layers are, for example, conjugated molecule layers, L gate layers composed of a different phthalocyanine which in their unmodulated state provide a substantial barrier to the interlayer transfer of electrons. When, however, an electric field or light, for instance, laser light, is applied in a plane perpendicular to the plane of the laminate, the L gate layers become conducting, permitting electrons stored in the L storage layers to pass through the L gate layers. This allows the devices to be modulated by an electric field, or by light to control the retrieval of information in the form of the electrons passed from layer-to-layer.
For such modulation to be practical, however, it is desirable that the phthalocyanine films employed be essentially devoid of regions that serve as neither storage nor gate regions such as regions of aliphatic chains previously referred to, since these would interfere with proper operation of the devices.
In view of the preceding, therefore, it is a first aspect of this invention to provide film structures comprising a plurality of parallel phthalocyanine layers in which the phthalocyanine rings of adjacent layers carry only hydroxo axial ligands.
A second aspect of this invention is to provide a process for hydrolyzing phthalocyanine films to convert the hydrophilic and hydrophobic ligands to hydroxo groups.
Another aspect of this invention is to provide phthalocyanine films useful in the fabrication of electronic devices modulated by electrical fields, or by light energy.
An additional aspect of this invention is to provide anisotropic phthalocyanine film structures.
A further aspect of this invention is to eliminate the hydrophobic axial ligands in phthalocyanine films through hydrolysis carried out during the coating of a substrate on a Langmuir-Blodgett balance.
Yet another aspect of this invention is to coat substrates on a Langmuir-Blodgett balance with a plurality of phthalocyanine film layers in which the phthalocyanine rings carry only hydroxo axial ligands.
Still a further aspect of this invention is to provide a substrate coated with phthalocyanine film layers that can be modulated with light or by electrical or magnetic fields to provide electronic devices.